1. Field of the Invention
The invention relates to grating light valve devices. More particularly, the present invention relates to grating light valve devices with an asymmetric configuration of movable ribbons for optimizing diffraction conditions which may be provided with a conductive trace to permit discharge or escape of electrical charges that may build up on the surface of a dielectric layer, and otherwise be trapped there, in the absence of the conductive layer.
2. Background of the Technology
Recent developments in the miniaturization of various electro-mechanical devices, also known as micro machines, has led to the emergence of miniature diffraction gratings. One type of miniature diffraction grating is a grating light valve. A grating light valve is a device that is capable of alternating between the conditions for constructive and destructive interference with an incident light source λ to modulate the reflected light source between a minimum and maximum intensity value, preferably in a stepwise fashion. Grating light valves have applications in display, print, optical and electrical device technologies. Examples of a grating light valves and their uses are disclosed in the U.S. Pat. No. 5,311,360 issued to Bloom et al., which is hereby incorporated by reference.
Referring to FIG. 1a, the grating light valve (GLV) construction as taught in U.S. Pat. No. 5,311,360, has a plurality of movable ribbons 100 that are spatially arranged over a substrate 102. The surfaces 104, corresponding to the ribbon tops and the regions of the substrate between the ribbons, are reflective. The surfaces 104 are made to be reflective by depositing a thin film of reflective materials, such as silver or aluminum on the substrate 102 and the ribbons 100. The ribbons and the substrate structure are micro fabricated from silicon-based materials. The height difference 103 between the reflective surfaces 104 of the substrate 102 and the reflective surfaces 104 of the ribbons 100 are configured to be λ/2 when the ribbons 100 are in the up position as shown in FIG. 1a. When light having a wavelength λ impinges on the compliment of reflective surfaces 104, light that is reflected from the surfaces 104 of the substrate 102 and ribbons 100 will be in phase. Light which strikes the reflective surfaces 104 of the substrate 102 travels λ/2 further than the light striking the reflective surfaces 104 of the ribbons 100. Then the portion of light that is reflected back from the reflective surfaces 104 of the substrate 102 returns traveling an addition λ/2 for a total of one complete wavelength λ. Therefore, the compliment of the reflective surfaces 104 function as a mirror to the incident light source with a wavelength λ.
By applying an appropriate bias voltages across the ribbons 100 and the substrate 102, a portion of the ribbons 100 move towards and contact the substrate 102, as shown in FIG. 1b. The thickness Tr of the ribbons 100 is designed to be λ/4 such that the distance 103′ is also λ/4. When light having a wavelength λ impinges on surfaces 104 and 104′ with the ribbons 100 in the down position, as shown in FIG. 1b, the portion of light reflected from the surfaces 104′ of the ribbons 100 will be out of phase with the portion of light reflected from the surfaces 104 of the substrate 102, thereby generating the conditions for destructive interference. By alternating the ribbons between the positions for constructive interference, as shown in FIG. 1a, and the positions for destructive interference, as shown in FIG. 1b, the grating light valve is capable of modulating the intensity of reflected light from an impinging light source having a wavelength λ.
In practice, the device is made by taking advantage of selective etching of a sacrificial polysilicon layers, which is blocked by a dielectric layer underneath. Charge or potential can rapidly build up on the surface of the dielectric layer. While larger, conventional IC's may be insensitive to such “trapped charges,” on the surface of the dielectric, even a very small charge potential may negatively impact the performance of a zero order GLV.